Surface Treatments & Finishes For Metals & Alloys (AQA GCSE Design & Technology): Revision Note
Exam code: 8552
Dip coating
Dip coating covers a heated metal part with a polymer coating
The cleaned metal is heated and dipped into fluidised polymer powder
Powder melts onto the surface and the part is removed and cooled
This creates a thick, comfortable and corrosion-resistant coating, for example on tool handles
The dip coating temperature range is 250-400°C
Over 400°C and the powder will catch fire or drip
Below 250°C and the finish will have an orange peel texture or will not adhere to the surface
Worked Example
State one reason for applying dip coating to a product.
[1 mark]
Answer
Creates a thick, comfortable and corrosion-resistant coating, for example on tool handles. [1]
Powder coating
Powder coating uses electrostatic charge to attract dry polymer powder to metal before heat curing
The metal is cleaned, powder is sprayed electrostatically, and the part is baked so the powder flows into a continuous film
Produces a durable, even coating with little solvent
This allows unused powder to be recovered
Galvanising
Galvanising coats steel or iron with zinc, commonly by hot dipping
The metal is cleaned and immersed in molten zinc, then removed and cooled
Zinc forms a barrier and sacrificially corrodes before the steel, giving strong rust protection
Examiner Tips and Tricks
Questions on metal finishes are commonly worth up to 6 marks for describing how a treatment is produced, not why it's used. Stating only the benefit (e.g. "it resists corrosion") scores zero. For dip coating, powder coating or galvanising, sequence your answer: how the metal is cleaned and prepared, the equipment and temperatures used, how the coating is applied, and how the part is cooled or cured.
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